In a tiny hall in Nasarallah, a poor agricultural village in the hills beyond Tunisia's historic Islamic city of Kairouan, Jamila Brahid is irate. Sitting in a huddle of country women wearing traditional rural headscarves, the 50-year-old villager is proud to have had a primary school education in a place where many of her female friends – mostly seasonal fruit-pickers – cannot read or write. A carpet-weaver who owed debts on wool and has never married because of her obligations looking after elderly relatives, she gives thanks for Tunisia's prized status as the most feminist country in the Arab world. But, she says, Sunday's elections will be the true test.

"The men are all sitting in cafes. The women do all the work, in the fields, as well as the home, earning money, making bread, providing for and taking care of the whole family," she says. "At least now we've got freedom of speech. Who says poor rural women aren't interested and won't vote? We're mobilised. We've been oppressed for too long."

The future of Tunisian women is a key issue in the elections – the first vote of the Arab spring. Tunisia's famously advanced women's rights are at the heart of secular nervousness over whether this open, liberal society will vote in huge numbers for the Islamist An-Nahda party, and whether that party, which says it is moderate and devoted to women's equality, could begin to chip away at women's status.

Tunisia, the only Arab country to ban polygamy, prides itself as the most feminist country in the region. In 1956, after independence from the French, women's rights were enshrined in law, banning multiple marriages and forced unilateral divorce. There is a minimum marriage age of 18 and rights for divorced women which are unprecedented in the Arab world. Women in headscarves rub shoulders with others in tight jeans and loose hair. More than 80% of adult females are literate, the contraception rate is high and women make up half the student population, a third of magistrates and a quarter of the diplomatic corps.

Tunisia's elections should be a great day for Arab women, but feminists are deeply anxious. Much-vaunted electoral rules on running equal numbers of men and women candidates have been downplayed by parties who suggest that in Tunisia's first ever free elections, voters simply "prefer" men to women candidates. This means the new assembly which will rewrite the constitution could be more than ever dominated by men.

Kairouan, the picturesque holy city and the first Islamic city in the Maghreb, is surrounded by poor, isolated villages where literacy is low and people make a scarce living from olives and citrus fruit. Typically of Tunisia, families are a patchwork: atheist communist women with loose hair have relatives who wear a headscarf and intend to vote Islamist.

"Don't sell your vote, vote from your heart, I'm speaking from mine when I say we need equality," Fathia Mahfoudhi, a secondary school sports teacher, tells the women gathered in the village hall in Nasarallah. She is standing for the Modernist Democratic Pole, a coalition of leftists, independents and feminists who seek to counter An-Nahda, saying religion and politics don't mix.

Mahfoudhi makes a moving speech with no notes. But outside, a male relative complains that as a man, he should have written her speech for her.

Later, an all-women group of campaigners and candidates decide not to have lunch openly in a restaurant. "People might not vote for us if we do. That's the reality of conservative village life," one says.

The commission reforming Tunisia's electoral landscape for the elections ruled earlier this year that there must be 50% parity between men and women on electoral lists – and not just women on the bottom rung: they must alternate with male candidates from the top of each party selection and share the most important roles. In the event this has not worked. Women make up only 6% of the leading candidates at the top of party selections, which means very few have a chance of winning a seat. Only the Modernist Democratic Pole has an equal number of women to men in top positions.

This is catastrophic, warns Sana Ben Achour of Tunisia's influential Association of Women Democrats. Women had been key players in the uprising which launched the Arab spring: from the highly-educated female elite of doctors, barristers and university professors to the huge numbers of unemployed female graduates. Most assumed they would easily take their place in the new democracy.

Many parties insist that people prefer to vote for men, including the centrist secular PDP, which is running few women at the head of its lists. An-Nahda is only running two leading women out of a total of 33 constituencies. The most high-profile is Souad Abderrahim, a pharmacist who does not wear a headscarf, running in a key Tunis constituency where leading figures from secular parties are standing. It is a public relations coup for a party which wants to show it is moderate. But Rachid Ghannouchi, the party leader, has spoken of a "reality" in which "the Tunisian woman has not yet acquired leadership status".

Anissa Saidi, a feminist and philosophy teacher running for the Modernist Democratic Pole in Kairouan, says: "We want equality enshrined in the constitution, we want laws against domestic violence." She fears An-Nahda's moderate discourse in support of women's rights might mask a fundamentalist strain which wants to make women work part-time to ease unemployment, or lessen education for girls.

Said Ferjani, of An-Nahda's central political bureau, says women's rights and education are paramount. "And in our programme it states we should not compel women to wear any kind of clothing, it's up to women to choose to put on a scarf or not, that's her business," he adds.

Even among secularists the feminist struggle in Tunisia is far from over. Of the country's young, well-educated unemployed‚ whose grievances sparked the uprising‚ two-thirds are women. There is still gross inequality in inheritance laws favouring sons and inequality of pay.

After the revolution feminists don't want women's rights to once again be used as a front.

Under Ben Ali feminism had become a double-edged sword. He headed the most repressive police state in the region, but if challenged on human rights abuses, horrific torture and a terrifying secret police, he would use his favourite calling card to the west: Tunisia was a modern "feminist state" where women were free, so things couldn't be that bad. He would argue that he had liberated women from the clutches of Islamism and sharia law. His wife, Leila Trabelsi, a hated figure who symbolised nepotism and corruption, headed several official women's rights bodies, awarding herself prizes for feminism, while grassroots feminist democracy campaigners were beaten in the street by police.

In Kairouan, Ahmed Kilan, the human rights activist who now heads the local arm of Tunisia's election body, says: "Some things in Tunisia just can't be touched. If anyone insisted women here must wear the veil, it's simple, people would be straight out onto the streets in protest."

Tunisians are about to vote in the region's first general elections since the Arab spring. We join Rabab Atiq as she campaigns for her father, a candidate for the Islamist An-Nahda party. Critics fear An-Nahda will reduce women's rights - but she believes it is the party of freedom